Preparation of bonded magnets (1) Process classification
Bonded magnets are composites composed of magnetic powders, binders, and appropriate additives. The magnetic properties of bonded magnets are mainly determined by the average performance of each magnetic powder with negligible interactions. Melting point metals or alloys are used as adhesives, but the adhesives used to form mass-produced bonded magnets are all polymer materials.
Differences between bonded magnets and sintered magnets
Unlike sintered magnets, the individual powder particles of bonded magnets must have sufficiently high coercive force. If the phase composition and microstructure required for high coercive force are severely damaged during the powder making process, good For bonded magnets, the coercive force has been greatly reduced due to the damage of the grain boundary phase and the oxidation of the particles.
Another major difference between bonded magnets and sintered magnets is that the magnetic properties are greatly reduced. We know that the maximum magnetic energy product of a magnet is proportional to the square of its remanence, and the remanence is related to the saturation magnetic induction, orientation and volume of the magnetic powder in the magnet. The filling rate is proportional, the binder and additives occupy a very considerable volume (close to 20%) in the bonded magnet, and many bonded magnets are not oriented, even for oriented magnets, the degree of orientation is difficult to achieve The same level as sintered magnets, so the performance of bonded magnets with the same volume is far inferior to that of sintered magnets.
Advantages of Bonded Magnets
Bonded magnets occupy an important position in the field of rare earth permanent magnets due to their advantages such as good performance consistency, precise size, complex shape, high material utilization rate, and easy integration with metal/plastic parts. The most important variety is the isotropic bonded magnet made of rapidly quenched NdFeB magnetic powder.
Preparation process and advantages and disadvantages of bonded magnets
According to the differences in the processing characteristics of polymer materials, the forming of bonded magnets can be divided into four categories: compression, injection, extrusion and calendering. The following figure is a schematic diagram of the four forming processes.
These four methods have their own advantages and disadvantages, and the specific application selection can refer to the following table: